1. Field of the Invention
The present invention relates to a method for measuring the respective heights of test parts, such as bonding wires, connected to a peripheral part of an object to be measured, such as an IC chip, and intervals between the wires, and a height-measuring apparatus for carrying out the method.
2. Description of the Prior Art
As shown in FIG. 12, an IC chip 6 bonded onto a lead frame 7 with an adhesive 9 is connected to other lead frames 7 with a plurality of bonding wires 8.
A wire-bonding operation for the connection of the bonding wires 8 is achieved by a wire-bonding apparatus. Wire-bonding conditions such as welded parts including balls 8a and crescents 8b, and the heights of the bonding wires 8 and intervals between the bonding wires 8 were visually inspected by using a magnifying glass or a microscope. Standard values for visual inspection are determined on the basis of the results of existence or non-existence of any failure of wire connection after the next resin molding process, and then the practical production of IC chips is started.
Since it is difficult to inspect the heights of three-dimensionally extended bonding wires by visual observation, it sometimes occurs that IC chips with defective connections are delivered to the next resin-molding process. If IC chips with defective connections are delivered to the resin-molding process, the bonding wires are broken by the flow of resin or the adjacent bonding wires are shorted in the resin-molding process, which results in production of defective IC chips.
Accordingly, it is a principal object of the present invention to provide a height-measuring method and a height-measuring apparatus capable of accurately and quickly measuring the heights of test parts and intervals between the test parts, which are difficult to measure through visual inspection.
Another object of the present invention is to provide a height-measuring method and a height-measuring apparatus capable of simply and accurately measuring the heights of test parts and intervals between the test parts, which are difficult to measure through visual inspection, to find and sort out defective objects at an early stage before a resin molding process.
To achieve the objects, there is provided a method for measuring a height of a test part of an object to be measured, including the steps of placing the object on a table, projecting a spot beam of a measurement light flux to the object on the table from an upper direction of the object, receiving a reflected light of the spot beam reflected by the object with a photosensor to detect a focused state of the measurement light flux on the object, driving the light source and the optical member relatively to the table in a way of scanning in a horizontal direction while reciprocating the optical member vertically at a high speed, and determining the height of the test part on the basis of a vertical position of the optical member when the measurement light flux is focused on the test part by the optical member.
Furthermore, there is provided an apparatus for measuring a height of a test part of an object to be measured, including a table on which the object is placed, a light source for emitting a light flux for measurement, a first optical system having an optical member for focusing, a first sensor for detecting a position of the optical member along the optical axis, a second sensor for receiving a reflected light of the light flux from the object, a second optical system for guiding the reflected light to the second sensor through the optical member, a case for housing the light source, the first optical system, the second sensor and the second optical system, a device for moving the optical axis relatively to the object by moving the case and the object relatively to each other at least in a horizontal direction, and an arithmetic control circuit for determining the height of the first optical system when the light flux is focused on the test part on the basis of a first detection signal output by the first sensor.